id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
21202	"Atomic masks fatal database errors and instead propagates ""connection already closed"""	Marti Raudsepp	Aymeric Augustin	"I noticed this problem with the new Atomic code in Django 1.6: when the PostgreSQL server raises a FATAL error (meaning that the server closes the connection after the error), then the Atomic block will swallow the original error and propagates a meaningless ""InterfaceError: connection already closed"" instead. I don't know whether this also affects other database backends.

I find that it's quite annoying to debug problems when the original cause of an error is hidden by subsequent error recovery code. It's not a new problem with Atomic, I believe commit_on_success (and Christophe Pettus's xact) had the same problem.

The easiest way to reproduce this is to terminate your own connection. (In PostgreSQL 9.1 and earlier you need to be superuser to do this):

{{{#!python
from django.db import connection
from django.db.transaction import atomic

with atomic():
    cur = connection.cursor()
    cur.execute(""select pg_terminate_backend(pg_backend_pid())"")
    cur.fetchall()
}}}

With current Django 1.6 this raises an error like:

{{{
Traceback (most recent call last):
  File ""term1.py"", line 7, in <module>
    cur.fetchall()
  File ""/home/marti/src/django/django/db/transaction.py"", line 351, in __exit__
    connection.set_autocommit(True)
  File ""/home/marti/src/django/django/db/backends/__init__.py"", line 335, in set_autocommit
    self._set_autocommit(autocommit)
  File ""/home/marti/src/django/django/db/backends/postgresql_psycopg2/base.py"", line 184, in _set_autocommit
    self.connection.autocommit = autocommit
psycopg2.InterfaceError: connection already closed
}}}

It tells you that the connection is closed, but not why. And there's a second problem too: a psycopg2 exception is propagated into user code, without using Django's exception wrappers.

To solve this problem, I submitted pull request 1696: https://github.com/django/django/issues/1696

 1. Changed BaseDatabaseWrapper.set_autocommit to wrap backend-specific errors.
 2. Wrapped `Atomic.__exit__` in another layer of try/except and re-raising the original exception in case of an InterfaceError.

Now the original exception is properly raised:

{{{
django.db.utils.OperationalError: terminating connection due to administrator command
}}}

I can also write unit tests if someone can help me figure out how to test this (the example I provided above requires PostgreSQL, with either superuser privs or version 9.2+).

Ran all 'transactions' and 'db_backends' tests on these changes with both SQLite (OK (skipped=42)) and psycopg2 (OK (skipped=1))
"	Cleanup/optimization	closed	Database layer (models, ORM)	1.6-beta-1	Normal	fixed		depaolim@…	Accepted	1	0	0	0	0	0